diff --git a/chartify.go b/chartify.go
index ec13432..b174408 100644
--- a/chartify.go
+++ b/chartify.go
@@ -382,13 +382,30 @@ func (r *Runner) Chartify(release, dirOrChart string, opts ...ChartifyOption) (s
 				"This may result in outdated chart dependencies.", release)
 		} else {
 			// Flatten the chart by fetching dependent chart archives and merging their K8s manifests into the temporary local chart
-			// So that we can uniformly patch them with JSON patch, Strategic-Merge patch, or with injectors
-			depArgs := []string{"dependency", "up", tempDir}
+			// so that we can uniformly patch them with JSON patch, Strategic-Merge patch, or with injectors.
+			//
+			// Use `helm dependency build` (honors Chart.lock) when a lock exists and no adhoc deps
+			// were injected; otherwise fall back to `helm dependency up` (re-resolves from Chart.yaml).
+			hasAdhocDeps := len(u.AdhocChartDependencies) > 0 || len(u.DeprecatedAdhocChartDependencies) > 0
+			useBuild := !hasAdhocDeps && hasChartLock(tempDir)
+			depCmd := "up"
+			if useBuild {
+				depCmd = "build"
+			}
+			depArgs := []string{"dependency", depCmd, tempDir}
 			// Helm 4 requires --plain-http for HTTP-only OCI registries
 			if u.OCIPlainHTTP && r.IsHelm4() {
 				depArgs = append(depArgs, "--plain-http")
 			}
 			_, err := r.run(nil, r.helmBin(), depArgs...)
+			if err != nil && useBuild && isLockOutOfSyncErr(err) {
+				// `helm dependency build` errors when Chart.lock is out of sync with Chart.yaml.
+				// Only fall back to `up` for this specific case — other errors (network, auth,
+				// missing artifacts) should surface to the caller rather than silently re-resolving.
+				r.Logf("`helm dependency build` failed for release %s (lock out of sync), falling back to `helm dependency up`: %v", release, err)
+				depArgs[1] = "up"
+				_, err = r.run(nil, r.helmBin(), depArgs...)
+			}
 			if err != nil {
 				return "", err
 			}
@@ -680,6 +697,27 @@ func (r *Runner) RewriteChartToPreventDoubleRendering(tempDir, filesDir string)
 	return nil
 }
 
+// hasChartLock reports whether a Chart.lock or requirements.lock file exists in the
+// given chart directory. Helm uses Chart.lock for apiVersion v2 charts and the legacy
+// requirements.lock for v1 charts; either is sufficient for `helm dependency build`.
+func hasChartLock(chartDir string) bool {
+	for _, name := range []string{"Chart.lock", "requirements.lock"} {
+		if _, err := os.Stat(filepath.Join(chartDir, name)); err == nil {
+			return true
+		}
+	}
+	return false
+}
+
+// isLockOutOfSyncErr returns true when the error from `helm dependency build` indicates
+// that the lock file is out of sync with Chart.yaml. Only this specific failure is safe
+// to recover from by falling back to `helm dependency up`.
+// Matches messages from Helm 3.x ("out of sync") and Helm 2.x ("lock file is out of date").
+func isLockOutOfSyncErr(err error) bool {
+	msg := err.Error()
+	return strings.Contains(msg, "out of sync") || strings.Contains(msg, "lock file is out of date")
+}
+
 func createDirForFile(f string) error {
 	dstFileDir := filepath.Dir(f)
 	if _, err := os.Lstat(dstFileDir); err == nil {
diff --git a/chartify_test.go b/chartify_test.go
index b78a9d1..1a559f2 100644
--- a/chartify_test.go
+++ b/chartify_test.go
@@ -2,8 +2,11 @@ package chartify
 
 import (
 	"context"
+	"fmt"
+	"io"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -114,6 +117,179 @@ func TestReadAdhocDependencies(t *testing.T) {
 	})
 }
 
+func TestDepCommandSelection(t *testing.T) {
+	newTestRunner := func(failBuild bool, failMsg string) (*Runner, *[]helmCall) {
+		var calls []helmCall
+		r := &Runner{
+			HelmBinary: "helm",
+			isHelm3:    true,
+			RunCommand: func(name string, args []string, dir string, stdout, stderr io.Writer, env map[string]string) error {
+				calls = append(calls, helmCall{name: name, args: append([]string{}, args...)})
+				if failBuild && len(args) >= 2 && args[0] == "dependency" && args[1] == "build" {
+					if _, err := stderr.Write([]byte(failMsg)); err != nil {
+						return err
+					}
+					return fmt.Errorf("%s", failMsg)
+				}
+				return nil
+			},
+			CopyFile:  CopyFile,
+			WriteFile: os.WriteFile,
+			ReadFile:  os.ReadFile,
+			ReadDir:   os.ReadDir,
+			Walk:      filepath.Walk,
+			Exists:    exists,
+			Logf:      func(string, ...interface{}) {},
+			MakeTempDir: func(release, chart string, opts *ChartifyOpts) string {
+				return ""
+			},
+		}
+		return r, &calls
+	}
+
+	setupChart := func(t *testing.T, withLock bool, lockName string) string {
+		t.Helper()
+		dir := t.TempDir()
+		chartYaml := filepath.Join(dir, "Chart.yaml")
+		if err := os.WriteFile(chartYaml, []byte("apiVersion: v2\nname: test\nversion: 0.1.0\n"), 0644); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.MkdirAll(filepath.Join(dir, "templates"), 0755); err != nil {
+			t.Fatal(err)
+		}
+		if withLock {
+			if err := os.WriteFile(filepath.Join(dir, lockName), []byte("dependencies: []\n"), 0644); err != nil {
+				t.Fatal(err)
+			}
+		}
+		return dir
+	}
+
+	t.Run("uses dependency build when Chart.lock exists and no adhoc deps", func(t *testing.T) {
+		chartDir := setupChart(t, true, "Chart.lock")
+		r, calls := newTestRunner(false, "")
+		r.MakeTempDir = func(_, _ string, _ *ChartifyOpts) string { return chartDir }
+
+		_, err := r.Chartify("rel", chartDir, WithChartifyOpts(&ChartifyOpts{}))
+		require.NoError(t, err)
+
+		depCalls := filterDepCalls(*calls)
+		require.Len(t, depCalls, 1)
+		require.Equal(t, "build", depCalls[0].args[1])
+	})
+
+	t.Run("uses dependency up when no lock file exists", func(t *testing.T) {
+		chartDir := setupChart(t, false, "")
+		r, calls := newTestRunner(false, "")
+		r.MakeTempDir = func(_, _ string, _ *ChartifyOpts) string { return chartDir }
+
+		_, err := r.Chartify("rel", chartDir, WithChartifyOpts(&ChartifyOpts{}))
+		require.NoError(t, err)
+
+		depCalls := filterDepCalls(*calls)
+		require.Len(t, depCalls, 1)
+		require.Equal(t, "up", depCalls[0].args[1])
+	})
+
+	t.Run("uses dependency up when AdhocChartDependencies present despite lock", func(t *testing.T) {
+		chartDir := setupChart(t, true, "Chart.lock")
+		r, calls := newTestRunner(false, "")
+		r.MakeTempDir = func(_, _ string, _ *ChartifyOpts) string { return chartDir }
+		r.Exists = func(path string) (bool, error) {
+			if _, err := os.Stat(path); err == nil {
+				return true, nil
+			}
+			return false, nil
+		}
+
+		_, err := r.Chartify("rel", chartDir, WithChartifyOpts(&ChartifyOpts{
+			AdhocChartDependencies: []ChartDependency{{Chart: chartDir, Version: "0.1.0"}},
+		}))
+		require.NoError(t, err)
+
+		depCalls := filterDepCalls(*calls)
+		require.Len(t, depCalls, 1)
+		require.Equal(t, "up", depCalls[0].args[1])
+	})
+
+	t.Run("uses dependency up when DeprecatedAdhocChartDependencies present despite lock", func(t *testing.T) {
+		chartDir := setupChart(t, true, "Chart.lock")
+		r, calls := newTestRunner(false, "")
+		r.MakeTempDir = func(_, _ string, _ *ChartifyOpts) string { return chartDir }
+		r.Exists = func(path string) (bool, error) {
+			if _, err := os.Stat(path); err == nil {
+				return true, nil
+			}
+			return false, nil
+		}
+
+		_, err := r.Chartify("rel", chartDir, WithChartifyOpts(&ChartifyOpts{
+			DeprecatedAdhocChartDependencies: []string{chartDir + ":0.1.0"},
+		}))
+		require.NoError(t, err)
+
+		depCalls := filterDepCalls(*calls)
+		require.Len(t, depCalls, 1)
+		require.Equal(t, "up", depCalls[0].args[1])
+	})
+
+	t.Run("falls back to up when build fails with lock out of sync", func(t *testing.T) {
+		chartDir := setupChart(t, true, "Chart.lock")
+		r, calls := newTestRunner(true, "the lock file (Chart.lock) is out of sync with the dependencies listed in Chart.yaml")
+		r.MakeTempDir = func(_, _ string, _ *ChartifyOpts) string { return chartDir }
+
+		_, err := r.Chartify("rel", chartDir, WithChartifyOpts(&ChartifyOpts{}))
+		require.NoError(t, err)
+
+		depCalls := filterDepCalls(*calls)
+		require.Len(t, depCalls, 2)
+		require.Equal(t, "build", depCalls[0].args[1])
+		require.Equal(t, "up", depCalls[1].args[1])
+	})
+
+	t.Run("does not fall back to up when build fails with non-sync error", func(t *testing.T) {
+		chartDir := setupChart(t, true, "Chart.lock")
+		r, calls := newTestRunner(true, "network timeout fetching dependency")
+		r.MakeTempDir = func(_, _ string, _ *ChartifyOpts) string { return chartDir }
+
+		_, err := r.Chartify("rel", chartDir, WithChartifyOpts(&ChartifyOpts{}))
+		require.Error(t, err)
+		require.Contains(t, err.Error(), "network timeout")
+
+		depCalls := filterDepCalls(*calls)
+		require.Len(t, depCalls, 1)
+		require.Equal(t, "build", depCalls[0].args[1])
+	})
+
+	t.Run("uses requirements.lock for legacy charts", func(t *testing.T) {
+		chartDir := setupChart(t, true, "requirements.lock")
+		r, calls := newTestRunner(false, "")
+		r.MakeTempDir = func(_, _ string, _ *ChartifyOpts) string { return chartDir }
+
+		_, err := r.Chartify("rel", chartDir, WithChartifyOpts(&ChartifyOpts{}))
+		require.NoError(t, err)
+
+		depCalls := filterDepCalls(*calls)
+		require.Len(t, depCalls, 1)
+		require.Equal(t, "build", depCalls[0].args[1])
+	})
+}
+
+type helmCall struct {
+	name string
+	args []string
+}
+
+func filterDepCalls(calls []helmCall) []helmCall {
+	var result []helmCall
+	for _, c := range calls {
+		if len(c.args) >= 2 && c.args[0] == "dependency" {
+			result = append(result, c)
+		}
+	}
+	return result
+}
+
 func TestUseHelmChartsInKustomize(t *testing.T) {
 	repo := "myrepo"
 	startServer(t, repo)
diff --git a/util_test.go b/util_test.go
index 6a944c4..8f171e8 100644
--- a/util_test.go
+++ b/util_test.go
@@ -1,11 +1,60 @@
 package chartify
 
 import (
+	"fmt"
+	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
 )
 
+func TestHasChartLock(t *testing.T) {
+	tests := []struct {
+		name     string
+		lockName string // empty means no lock file is created
+		want     bool
+	}{
+		{name: "no lock file", lockName: "", want: false},
+		{name: "Chart.lock present", lockName: "Chart.lock", want: true},
+		{name: "requirements.lock present", lockName: "requirements.lock", want: true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			dir := t.TempDir()
+			if tt.lockName != "" {
+				path := filepath.Join(dir, tt.lockName)
+				if err := os.WriteFile(path, []byte("dependencies: []\n"), 0644); err != nil {
+					t.Fatalf("writing fixture: %v", err)
+				}
+			}
+			if got := hasChartLock(dir); got != tt.want {
+				t.Errorf("hasChartLock() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestIsLockOutOfSyncErr(t *testing.T) {
+	tests := []struct {
+		name string
+		err  error
+		want bool
+	}{
+		{name: "out of sync message", err: fmt.Errorf("the lock file (Chart.lock) is out of sync with the dependencies listed in Chart.yaml"), want: true},
+		{name: "lock file is out of date", err: fmt.Errorf("lock file is out of date"), want: true},
+		{name: "network error", err: fmt.Errorf("network timeout fetching dependency"), want: false},
+		{name: "auth error", err: fmt.Errorf("401 unauthorized"), want: false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := isLockOutOfSyncErr(tt.err); got != tt.want {
+				t.Errorf("isLockOutOfSyncErr() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
 func TestCreateFlagChain(t *testing.T) {
 	testcases := []struct {
 		flag   string